Schmitt receiver systems and methods for high-voltage input signals

ABSTRACT

Presented systems and methods facilitate efficient switching operations for components operating at different voltage level than a received signal voltage level. In one embodiment, the components of a presented system are operable to perform switching operations for signals with a voltage level swing larger than the power rail of the circuit receiving the signals. In one embodiment a system includes an input component, a transition component, a transition point feedback component and an output component. The input component is operable to receive an input signal. The transition component is operable to transition the input signal. The transition point feedback component is operable to adjust a point at which a transition in the input signal occurs in the transition component. The output component is operable to forward an output signal from the transition point feedback component.

RELATED APPLICATIONS

The present application claims the benefit and priority of U.S. provisional application No. 61/697,283 (NVID-SC-11-0180-81-US-PRO), entitled “Schmitt Receiver for High-Voltage Input Signals And Core Voltage Reset Circuit With Wide Noise Margin,” filed on Sep. 5, 2012, which is incorporated herein by this reference.

TECHNICAL FIELD

The present disclosure relates generally to the field of integrated circuits and more specifically to the field of adjusting hysteresis and noise margins.

BACKGROUND

Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data in most areas of business, science, education and entertainment. These devices often include a plurality of power domains with some of the power domains operating at different voltages. Some conventional integrated circuits with split power rail approaches have different power domains receiving different power supply voltages from respective different power rails. Conventional attempts at coordinating operations at the different voltage levels can be complicated and problematic.

Various domains can include a variety of functional components configured to operate at the different respective voltage levels. Some traditional systems include domains with functional components configured to operate at a lower voltage level than another domain. Conventional coordination of operations in the two different domains can be problematic. In addition, some signals often have relatively large noise that can pose significant problems for some domains. Sometimes receiver circuits receive signals with higher voltage swing than a receiver's own voltage rail. For example, a receiver circuit operating on a relatively low voltage rail (e.g., 1.8V) may be required to receive a signal with a relatively high (e.g., 3.3V) voltage swing. This presents a challenge for noise margin, since a receiver operating with a low (e.g., 1.8V) power rail will exhibit noise margins (VIL/VIH) for a low (1.8V) signal swing. Meanwhile, a signal with a high swing (3.3V) would require noise margins for a high (3.3V) swing, which would be significantly wider than those for a low (1.8V) swing. Conventional approaches to handling different voltage domains are often limited and problematic. Some conventional approaches increase the voltage of the receiver to a higher voltage (e.g., 3.3V, etc.), which costs power and may require redesign. Other conventional approaches just accept the penalty to noise margin.

SUMMARY

Presented systems and methods facilitate efficient switching operations for components operating at a different voltage level than a received signal voltage level. In one embodiment, the components of a presented system are operable to perform switching operations for signals with a voltage level swing larger than the power rail of the circuit receiving the signals. In one embodiment a system includes an input component, a transition component, a transition point feedback component and an output component. The input component is operable to receive an input signal. The transition component is operable to transition the input signal. The transition point feedback component is operable to adjust a point at which a transition in the input signal occurs in the transition component. The output component is operable to forward an output signal from the transition point feedback component.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention by way of example and not by way of limitation. The drawings referred to in this specification should be understood as not being drawn to scale except if specifically noted.

FIG. 1 is a block diagram of a Schmitt trigger system in accordance with one embodiment of the present invention.

FIG. 2 is a block diagram of a Schmitt trigger system in accordance with one embodiment of the present invention.

FIG. 3 is a block diagram of Schmitt trigger method in accordance with one embodiment of the present invention.

FIG. 4 is an exemplary graph illustrating a hysteresis adjustment in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present invention. The drawings showing embodiments of the invention are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the invention can be operated in any orientation.

Notation and Nomenclature

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “processing” or “accessing” or “executing” or “storing” or “rendering” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories and other computer readable media into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. When a component appears in several embodiments, the use of the same reference numeral signifies that the component is the same component as illustrated in the original embodiment.

Presented systems and methods facilitate efficient increase in hysteresis. The presented systems and methods can increase the hysteresis by adjusting the noise margin, including adjusting the voltage input low (VIL) point and voltage input high (VIH) point. In one embodiment, the described systems and methods involve modification of a Schmitt receiver. The modification can increase noise margin for wider swing inputs. Using this design in one exemplary implementation, a Schmitt receiver operating on a relatively low (e.g., 1.8V, etc.) rail can receive a signal with a relatively high (e.g., 3.3V, etc.) swing while exhibiting noise margins for a high (e.g., 3.3V, etc.) signal, which are much wider than noise margins for a low (e.g., 1.8V, etc.) signal.

FIG. 1 is a block diagram of a Schmitt trigger system 100 in accordance with one embodiment of the present invention. Schmitt trigger system 100 includes an input component 110, a transition component 120, a feedback component 130 and an output component 140. Input component 110 and output component 140 are coupled to transition component 120 which is coupled to transition point feedback component 130.

The components of Schmitt trigger system 100 are operable to perform switching operations. Input component 110 is operable to receive an input signal. Transition component 120 is operable to transition the input signal. Feedback component 130 is operable to adjust a point at which a transition in the input signal occurs in the transition component. Output component 140 is operable to forward an output signal from the pull-up component.

It is appreciated a transition can be made to a variety of voltage levels (e.g., VDD, VDD-Vt, etc.). The transition point feedback component is operable to adjust a point at which a transition in the input signal occurs in a pull-up. In one exemplary implementation, the transition point feedback component is operable to adjust a point at which a transition in the input signal occurs in the transition component. In one embodiment, the transition point feedback component is operable to adjust a point at which a transition in the input signal occurs in a pull-down.

Typically, Schmitt trigger points can exhibit hysteresis at 33%*VDDC (resulting in VIL) and 66%*VDDC (resulting in VIH). However, if VDDC=1.8V then this would make VIL far too low for a signal swing of 3.3V, which would require a VIL of 33%*(3.3V)=1.0V. This is approximately ˜50%*VDDC of 1.8V, significantly higher than regular Schmitt trigger points on the 1 to 0 transition. Furthermore, the required VIH of a 3.3V Swing signal, 66%*3.3V=2.2V, is above the VDDC of 1.8V. This is very difficult or impossible to achieve with a regular Schmitt Trigger.

The design uses feedback to adjust (e.g., increase, decrease, etc.) VIH, VIL or both. It is appreciated that VIL adjustment can also be achieved using adjustment in relative device sizing (e.g., making a pull-up component stronger than a pull-down component, etc.). Due to hysteresis, in one embodiment the input to the inverter would be full rail (HIGH or LOW) except at the Schmitt trigger points.

FIG. 2 is a block diagram of a Schmitt trigger system 200 in accordance with one embodiment of the present invention. Schmitt trigger system 200 includes an input component 210, a pull-up component 220, a pull-down component 230, a feedback component 240, and an output component 250. Input component 210 is coupled to pull-up component 220 and pull-down component 230 which are coupled to output component 250. Feedback component 240 is coupled to pull-up component 220. In one embodiment, the pull-up component 220 includes a PMOS component and the pull-down component 230 includes an NMOS component.

The components of Schmitt trigger system 200 cooperatively operate to invert signals with relatively large swings and wide noise margins. Input component 210 is operable to receive an input signal. Pull-up component 220 is operable to transition the input signal up (e.g., from a low to high, logical 0 to logical 1, etc.). Pull-down component 230 is operable to transition the input signal down (e.g., from a high to low, logical 1 to logical 0, etc.). Feedback component 240 is operable to adjust the voltage at which the pull-down component 230 allows transitions. In one exemplary implementation, it increases the voltage at which the pull-down component 230 is able to transition the output component 250 from 1 to 0. Output component 250 is operable to forward an output signal from the feedback component.

In one embodiment, the pull-up component 220 is associated with VIL. The pull-up component 220 pulls up to VDD. In one exemplary implementation, the pull-up component 220 transitions the output signal from logical 0 to logical 1 as the input signal transitions from logical 1 to logical 0 and passes approximately 33% of VDD. In one embodiment, VIL can be 50% of VDD. In one exemplary implementation, the pull-up component 220 can transition the input signal within a range (e.g., 28% to 37% of VDD, etc.).

In one embodiment, the pull-down component 230 is associated with VIH. The pull-down component 230 pulls down to ground. The pull-down component 230 transitions the output signal from logical 1 to logical 0 as the input transitions from logical 0 to logical 1 and passes at approximately 66% of VDD. In one exemplary implementation, the pull-up component 220 can transition the input signal within a range (e.g., 62% to 70% of VDD, etc.). In one embodiment, VIH is higher than VDD.

In one embodiment, the feedback component 240 resists a transition of the input signal by the pull-down component. Resisting the transition enables the VIH to be adjusted (e.g., increased, etc.).

In one embodiment, on logical 1 to logical 0 transitions, the input to the inverter is logical 0, so the pull-up PMOS 241 of feedback component 240 is off and exerts no influence. The Schmitt trigger point on logical 1 to logical 0 transitions can be made approximately ˜50%*VDDC by making PMOS1, PMOS2, and NMOS3 large relative to NMOS1, NMOS2, and PMOS3. In one exemplary implementation, this can be made to produce VIL=33%*3.3V, which is appropriate for 3.3V swing signals.

In one embodiment, the strength of the pull-up component 220 is relatively large compared to the pull-down component. In one exemplary implementation, VIL is adjusted higher by the pull-up component interaction with the pull-down component. In one embodiment, on logical 0 to logical 1 transitions, the input to the inverter is “1” and the Pull-up PMOS 241 in feedback component 240 is ON. In one exemplary implementation, this means that even as the input signal passes VDDC=1.8V (so that PMOS1 and PMOS2 are OFF) NMOS1 and NMOS2 continue to pull-down against the Pull-up PMOS to pull the receiver's output to LOW. Once that happens, the Pull-up PMOS is turned OFF. This way, VIH can be made higher than VDDC and can be made to be 66%*3.3V, which is appropriate for 3.3V signals.

FIG. 3 is a block diagram of Schmitt trigger method 300 in accordance with one embodiment of the present invention.

In block 310, a signal is received. It is appreciated that the received signal can be relatively low or relatively high. In one embodiment, the relatively low corresponds to a logical 0 and the relatively high corresponds to a logical 1.

In block 320, a state of the signal is transitioned. A transition can include a pull-up, a pull-down, or both. In one embodiment, a pull-up transition includes changing a relatively low voltage input to a relatively high voltage output. In one exemplary implementation, the pull-up corresponds to a transition from a logical 0 to a logical 1. In one embodiment, a pull-down transition includes changing a relatively high voltage input to a relatively low voltage output. In one exemplary implementation, the pull-down corresponds to a transition from a logical 1 to a logical 0.

In block 330, a point at which a transition of the input signal occurs is adjusted. In one embodiment, the adjusting is performed by feedback. In one exemplary implementation, the feedback fights the transition. The adjustment can include adjusting VIH, VIL of both. The adjusting can include widening a hysteresis range.

In block 340, a signal is output after the transition.

In one embodiment, there is a circuit operating in a 1.8 V rail domain receiving a signal that with a 3.3 V swing. The present systems and methods adjust the VIL and VIH appropriately for 33% of 3.3 instead of 33% of 1.8. FIG. 4 is an exemplary graph illustrating a hysteresis adjustment in accordance with one embodiment of the present invention. For example, the VIL of one third of 3.3 V (e.g., 1.1 V) is adjusted to one third of 1.8 V (e.g., 600 mV) and the VIH of two thirds of 1.8V (e.g., 1.2 V) is adjusted to two thirds of 3.3 V (e.g., 2.2). Thus the system can operate with a voltage swing value that is higher than the voltage rail itself.

It is appreciated that presented systems and methods can use feedback to increase hysteresis. The feedback can adjust the relative value of VIH and VIL or both. In one embodiment, the feedback can adjust the noise margin.

It is appreciated that the feedback a conventional Schmitt trigger component may have a characteristic that may be considered a feedback and that the present feedback described herein is different or in addition to feedback characteristics that a conventional Schmitt trigger component may have. In one embodiment, the feedback of a presented system fights a transition with additional feedback than in conventional Schmitt trigger systems and facilitates greater flexibility in adjusting a VIL, a VIH, or both.

Thus, the presented systems and methods facilitate efficient increase of hysteresis. The presented systems and methods can increase the hysteresis by decreasing the voltage input low (VIL) point and increasing voltage input high (VIH) point. The modification can enable a receiver operating on a relatively low voltage (e.g., 1.8V, etc.) rail to receive a signal with a relatively high (e.g., 3.3V, etc.) swing that exhibit noise margins for a high (e.g., 3.3V, etc.) signal.

Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. It is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law. 

What is claimed is:
 1. A Schmitt trigger system comprising: an input component operable to receive an input signal; a pull-up component operable to transition the input signal; a feedback component operable to adjust a voltage in a high point at which a transition in the input signal occurs in the pull-up component; and an output component operable to forward an output signal from the pull-up component.
 2. The Schmitt trigger system of claim 1 the feedback component increases the voltage level of VIH.
 3. The Schmitt trigger system of claim 2 wherein the pull-up component transitions the input signal within a range of 62% to 70% of VDD.
 4. The Schmitt trigger system of claim 1 wherein VIH is higher than VDD.
 5. The Schmitt trigger system of claim 1 wherein the feedback component resists a transition of the input signal by the pull-down component.
 4. The Schmitt trigger system of claim 1 further comprising a pull-down component, wherein the strength of the pull-up component is relatively large compared to the pull-down component.
 7. The Schmitt trigger system of claim 1 wherein VIL is adjusted higher by the pull-up component interaction with the pull-down component.
 8. The Schmitt trigger system of claim 1 wherein the pull-up component includes a PMOS component.
 9. The Schmitt trigger system of claim 1 wherein the pull-down includes an NMOS component.
 10. A Schmitt trigger method comprising: receiving a signal; transitioning a state of the signal; adjusting a point at which a transition of the input signal occurs; and outputting a signal after the transition.
 11. A Schmitt trigger method of claim 10 wherein the adjusting is performed by feedback.
 12. A Schmitt trigger method of claim 10 wherein a VIH is adjusted.
 13. A Schmitt trigger method of claim 10 wherein a VIL is adjusted.
 14. A Schmitt trigger method of claim 10 wherein a hysteresis range is widened.
 15. A Schmitt trigger method of claim 10 wherein the adjusting is performed by feedback that fights the transition.
 16. A Schmitt trigger system comprising: an input component operable to receive and input signal; a transition component operable to transition the input signal; a transition point feedback component operable to adjust the voltage at which the transition component allows transitions; and an output component operable to forward an output signal from the transition point feedback component.
 17. The Schmitt trigger component of claim 16 wherein the transition is to VDD.
 18. The Schmitt trigger component of claim 16 wherein the transition is to VDD-Vt.
 19. The Schmitt trigger component of claim 16 wherein the transition point feedback component operable to adjust a point at which a transition in the input signal occurs in a pull-up.
 20. The Schmitt trigger component of claim 16 wherein transition point feedback component operable to adjust a point at which a transition in the input signal occurs in the transition component transition point feedback component operable to adjust a point at which a transition in the input signal occurs in a pull-down. 